Aniline Bronsted acid

Cations of weak bases (i.e. Bronsted acids such as the phenylammonium ion C6H5NH3) may be titrated with strong bases, and the treatment is similar. These were formerly regarded as salts of weak bases (e.g. aniline (phenylamine), Kb = 4.0 x 10 10) and strong acids an example is aniline hydrochloride (phenylammonium chloride). 

The catalytic activity for the aniline formation from chlorobenzene and ammonia of the Y zeolites with various cations was studied at 395° C (Table I). It is clear that the transition metal-exchanged zeolites have the catalytic activity for the reaction, while alkali metal and alkaline earth metal zeolites do not. The fact that alkaline earth metal-exchanged zeolites usually have high activity for carbonium ion-type reactions denies the possibility that Bronsted acid sites are responsible for the reaction. Thus, catalytic activity of zeolites for this reaction may be caused by the... 

Li et al. [93] have used l-ethylimidazolium trifluoroacetate, which is a Bronsted acidic ionic liquid, as a medium for the electropolymerization of aniline. They report that in this ionic liquid the oxidation potential of aniline is lower (0.58 V compared to 0.83 V in 0.5 M H2SO4) and that the growth rate of the polymer is increased. Further, the resultant films are smooth, strongly adhered to the Pt working electrode and are very electrochemically stable. Similar results have been reported by Liu et al. [92], who found that this was the best ionic liquid for the polymerization of aniline, compared to the unsatisfactory results observed in other protic ionic liquids 1-butylimidazolium tetrafluoroborate, 1-butylimidazolium nitrate and 1-butylimidazolium p-toluenesulfonate, as well as the l-butyl-3-methylimidazolium hydrogen sulfate and l-butyl-3-methyimidazolium dihydrogen phosphate. 

Akiyama et al. have reported that the cycloaddition of 102 to imines is effectively accelerated by 10 mol% of a Bronsted acid such as HBF4 in aqueous media, affording dihydro-4-pyridones in good to high yield (Scheme 10.109) [295]. This catalytic system is applicable to three-component synfhesis of dihydro-4-pyridones from aldehydes, anilines, and 102. The three-component coupling can be achieved efficiently in water without any organic solvent by using SDS as surfactant. 

Conclusions can be drawn concerning the nature of the specific centers on silica-alumina from the similarity of the spectrum of adsorbed aniline with that of benzene. These centers may be of two types, either Bronsted acids or Lewis acids, and may be depicted as shown in structures... 

Structure A can easily give up its weakly bound proton and hence function as a Bronsted acid. Structure B possesses electron-accepting properties by virtue of the aluminum atom which contains an empty -orbital. Reversion of the aniline spectrum to that of benzene will occur when the excess electron density distributed to the ring by the amino group becomes localized on the nitrogen atom. Thus proton addition to the amino group in aniline produces the anilinium ion whose... 

Most osmium complexes of phenols [26,44], anilines [24,45], and anisoles [23, 46,47] undergo electrophilic addition with a high regiochemical preference for para addition. While electrophilic additions to phenol complexes are typically carried out in the presence of an amine base catalyst, the other two classes generally require a mild Lewis or Bronsted acid to promote the reaction. The primary advantage of the less activated arenes is that the 4H-arenium species resulting from electrophilic addition are more reactive toward nucleophilic addition reactions (see below). 

Quinolines are prepared by the Skraup process of combining glycerol with anilines (Scheme 54).The ionic liquid, l-(l-alkylsulfonic)-3-methylimidiazolium chloride, serves as both the solvent and the Bronsted acid catalyst.The glycerol is converted to acrolein under acid catalyst, which goes more efficiently, in both a shorter time and yields, with the ionic liquid catalyst (14TT3319). 

The Povarov reaction is the inverse electron-demand aza-Diels-Alder reaction, a [4 + 2] cycloaddition between an A-arylimine (as the diene) and an electron-rich olefin (as the dienophile), which gives tetrahydroquinolines 3 or substituted quinolines 4 as the product. This reaction also called as imino-Diels-Alder reaction, usually catalyzed by Lewis or Bronsted acids. Since the jV-arylimine can be prepared in situ from aniline and aldehyde, thus the Povarov reaction can be performed in a one-pot fashion. ... 

By combining regioselective Au(l)-catalyzed enamine synthesis with enantiose-lective transfer hydrogenation, the asymmetric synthesis of tetrahydroquinolines from simple 2-(2-propynyl)aniline derivatives has been achieved (Scheme 15.94). Here, a chiral Bronsted acid is used in combination with the Hantzsch ester to install the chiral center with up to 99% ee [316]. 

The change of the orientational control by amino substituents in acid media or on complex formation is obviously supported by the bromination of iV,i T-dimethylaniline in sulfuric acid containing silver sulfate, which produces 60% of 3-bromo- and 20% 4-bromo-iV,i T-dimethylaniline . This result, again seemed to suggest that the appreciable para product in acidic halogenation of aromatic amines may be due to an ion-pair mechanism or to partial dissociation to the free base . Yet the formation of para products in the presence of excess of strong Lewis or Bronsted acid with aniline, could hardly indicate the presence of free amine, and there is evidence that electrophilic bromine attack, at the meta as well as at the para positions, occurs on deactivated anilinium ions . 

Yu et al. [214] investigated a related transformation with anilines in place of ammonium acetate, involving two equivalents of dimedone to afford acridines 126 (Scheme 69). They used a dimeric Bronsted acid IL containing perflu-oroalkyl tails in 1.5 mol% under refluxing condition for 4h to afford acridines in 79-91% yield. The catalytic medium was recycled and reused many times with no appreciable decrease in yield. The electronic nature of substituents present on aromatic aldehydes seldom affected the yield of products however access to acridines was limited to nucleophilic anilines such as para-toluidine and para-anisidine [214]. 

In 2009, Peris et al. reported the henzylation of arenes using complex 35b as catalyst (0.1 or 1 molyo). " Different benzylating agents such as benzyl alcohols, benzyl ethers or styrene derivatives were used in combination with toluene, xylenes, phenol and anisole [eqn (8.16)]. Catalyst 35b displayed high activities, except for a few cases, but poor selectivities for the ortholpara isomers were observed (40 60 to 10 90). Although a mixture of orthol N-alkylated/para products was obtained when anilines were used as substrates, the results compared well with those previously reported which made use of Bronsted acids or metal complexes as catalysts. 

To date, there is only one example of enantioselective Af-allqvlation by means of hydrogen borrowing. Zhao and co-workers discovered a chiral iridium catalyst/chiral Bronsted acid combination that enables the N-allqv-lation of racemic secondary alcohols with anilines to provide secondary amines, with greater than 90% ee in many cases (Scheme 12.12). Attempts to extend the scope of the amine reactant resulted in poor enantioselectivity. 

The Bronsted acid (274) catalysed asymmetric tandem 1,5-hydride transfer/ring closing reaction of o-aminobenzo-a-ketoesters (271) with anilines (272), gave cyclic aminals (273) in fairly good diastereo- and enantioselectivities (Scheme 70). ... 

This reaction is restricted to derivatives of N-benzylideneaniline since cyclohexane carbaldehyde or pivaldehyde with aniline give the product in less than 10% yield. More surprisingly, the reaction of acylzirconocene chloride 38 with imine proceeds with a Bronsted acid, even in aqueous media. Although, the hydrolysis of acylzirconocene into aldehyde is a well-known process (see Scheme 12.22), the reaction with N-phenyl imine is much faster. Under 20mol% HCl/THF, the... 

In the first instance, acidity influences the acid-base equilibria of the reactants. The amine is a Bronsted base. Aniline, a typical substrate, has pKa = 4.6, which means that the protonation shown in Scheme 3-11 is almost complete under normal conditions of diazotization (pH < 1). The base is definitely a much better reagent than the anilinium ion for nitrosation because the latter is an electrophilic substitution. One expects — simply on the basis of the equilibrium shown in Scheme 3-11 — that the rate of diazotization should decrease linearly with increasing acid concentration or, at higher acidities, with the Hammett acidity function h0 (for acidity functions see Rochester, 1970 Cox and Yates, 1983). 

Fig. 11.5 (A) Eigen-type plot for the general base-catalysed reactions of 4-chlorobenzaldehyde with a substituted hydrazine [8] the line is calculated from log kg = —0.341 log(1 + 106 09 pffa). (B) Eigen-type plot for general acid catalysis in the reaction of cyanic acid (HNCO) with aniline, and an alternative interpretation [9] the dashed line has a Bronsted slope of —0.19 and the break at p/fa near 10 in the solid line is consistent with proton transfer to an addition intermediate (PhNH2+CONH ).

Bronsted plots with some scatter should always be examined carefully because they might conform with the Eigen equation. A classic case is the acid-catalysed reaction of aniline with HNCO which can be fitted to a shallow Bronsted line (slope = —0.19)[9] however, the data are also consistent with an Eigen dependence (Fig. 11.5B) arising from a mechanism involving trapping of an addition intermediate by proton transfer (Scheme 11.11). 

Fia. XVI. 1. Bronsted plot for the base-catalyzed decomposition of nitramide. (Data from compilation by R. P. Bell, Acid-Base Catalysis, Oxford University Press, New York, 1941.) + Doubly charged bases, B++, mostly aquo-iona, [M(H20) (0I1)]++. o Doubly charged bases, B". o- Uncharged bases, B° all substituted anilines. 

The reaction in aqueous solution is general acid catalyzed and the Bronsted coefficient for variation in the aniline substituent is constant, being fix = 0.66 when the acid is oxonium ion. The Bronsted coefficient for varying the general acid when aniline is kept constant is —0.54 for 4-sulfanilic acid. According to the empirical rate law obeyed (equation 11),... 

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